フリー問題

問題文

A list has to keep every product even when no order refers to it. The author writes an outer join but the products without orders are still missing. What went wrong?

選択肢

1. The join was written between the wrong columns so the rows without a partner were dropped and the ones with a partner were duplicated.
2. The side that was chosen for preservation was the products rather than the orders so the rows without a partner were dropped by the row filter that followed.
3. The side that was marked for preservation was the orders rather than the products so the rows without a partner were dropped from the side that mattered.
4. The join was written with a condition on both sides so the rows without a partner were dropped even though the outer form had been used.